Tuesday I told you I’d explain the reasoning behind the fuse holder having a melt down and the fuse not being affected at all. The fuse shown in that photo (see below) had been subjected to a DC load (in amperes) at or near its nominal trip rating for an extended period of time. A real world example of this would be the DC supply fuse for something like an inverter installation with continuously running AC appliances. The fuse in that situation may get hot enough to cause a melt down of the fuse holder and maybe even some of the wire insulation near the termination points at the fuse holder. Wayne Kelsoe and I were curious about how long this might take so one of the experiments we conducted in his lab was to hook up a variable load machine to a typical ANL fuse assembly and track the temperature rise over time. In our test we were never able to actually melt the fuse holder (high quality material selection on the part of the manufacturer) but we do know for sure that not all fuse holders are cut from the same cloth, as evidenced by the photo in yesterday’s post and many others in our collection.
The question becomes how do you avoid this type of situation? The best solution is not to load fuses continuously at anywhere near their nominal trip point. Additionally, make sure the wire gauge you select is if anything oversized in high current draw situations. Larger wire will do a better job of conducting the heat away from the termination points at the fuse holder. In the video below, Wayne Kelsoe, chief technology officer for Blue Sea Systems in Bellingham, Washington provides a short explanation of what we are doing and what we expect to happen: